1. Field of the Invention
The present invention relates to filter systems. This invention is directed toward an improved underdrain system that may be used in granular filtration media systems. More particularly, the improvement is a pre-fabricated cell system that allows direct installment of an underdrain of a filter.
2. Discussion of the Related Technology
Traveling bridge filter systems are well known in the field of waste water management. These systems are exemplified in U.S. Pat. No. 3,239,061, U.S. Pat. No. 4,152,265, and Assignee's U.S. Pat. No. 5,234,600 the disclosures of which are expressly incorporated by reference herein. The success of such filters depends to a large extent on the filter system's ability to backwash small, individual sections (often referred to as cells) of granular filtration media with water to periodically clean the filtration media. This backwash water is the waste by-product of filtering. Conventional filter systems backwash the entire filter area, thus requiring large flow rates and large volumes of backwash water. By minimizing the area of the filtration media to be cleansed using a cell structure, the amount of waste by-product, which is directly proportional to the area of the filtration media being cleansed, is also minimized. Sand is, commonly, used as a filtration media.
Conventionally, the construction of individual cells for containing a limited amount of filtration media uses fiberglass-reinforced polyester (FRP) sheets as cell dividers, plastic end sections, FRP support angles (either integral to cell dividers or attached separately), FRP holddown angles, porous media support plates, adhesive/sealant, a variety of hardware types, and leveling channels. This equipment is used to construct individual cells that are substantially hydraulically separated from other cells. In the present art, the cell dividers are used to:
(1) divide the filtration media into individual compartments; PA1 (2) form the sidewalls of the plenum compartments; and PA1 (3) support the porous plates. PA1 (1) marking the locations of leveling strips, drilling holes, and placing anchor bolts in the filter tank bottom to support ends of leveling strips; PA1 (2) installing leveling strips in order to provide a level base for the cell dividers; PA1 (3) compensating for any irregularities in the base slab by using a surveyor's level, placing shims under the anchor bolts and at a midpoint between the anchor bolts, leveling all of the leveling strips to within 1/16th of an inch; PA1 (4) creating a multitude of individual compartments within the tank by mounting cell dividers on the leveling strips using an attachment angle and attaching cell end sections on both ends of the cell using stainless steel hardware; PA1 (5) installing filtrate spools at the outlet end of the cells; and PA1 (6) filling the compartments formed by the cell dividers with grout up to the level of the invert of the filtrate spool. PA1 (1) installing porous media support plates at the top of the plenum compartment by first placing a generous amount of sealant/adhesive on a support angle along the entire periphery of the cell; PA1 (2) placing the support plates on the support angle, being careful to space the plates end to end; PA1 (3) placing a generous amount of sealant/adhesive on the top of the porous media support plate along the entire periphery of the cell; and PA1 (4) placing a holddown angle in position and attaching it with stainless steel hardware. Installing the plates involves applying sealant, which must be installed between a temperature range of 40 F. to 95 F. under varying weather conditions, which affects the viscosity of the sealant and makes it difficult to obtain consistent results from job to job.
This multiple utility requires that great care be taken to avoid installation errors so that all the required purposes are properly met.
The installation of prior filters requires many steps and hardware; some steps require the presence of a technician. Initially, the concrete bottom of a filter tank is constructed, usually by a contractor. After the bottom of the filter tank (also called the "slab") is constructed, the slab is cleared, and multiple cell dividers and cell end sections are installed in the tank. Conventional cell installation requires the steps of:
Also, the top surface of the grout is sloped to encourage filtrate to drain downwards toward the cell outlets.
At this point, the concrete equipment returns to the site and is used to build the forms for making the concrete walls of the filter tank. The end sections, and only the end sections, of the cells must be cast into the walls of the tank, which makes building the forms for the walls quite difficult. After the concrete tank is completed, the contractor arranges porous media support plates in the cells. The steps involved include:
After installing the porous plates, a "light test" is performed. This test must be performed when the sun is down, preferably at the darkest time of the night. During the test, a bright light is inserted into the plenum under the porous plates. As the light is withdrawn from a cell, an observer on the top side of the porous plates watches for any light to shine through, which indicates a leak that filtration media could pass through. The light spots, which commonly occur even with careful workmanship, must be repaired by topically applying additional sealant/adhesive. Finally, filtration media may be placed in the cell compartments to complete the construction of the filter's underdrain.
This method of construction has numerous drawbacks. Portions of the underdrain must be installed after the concrete filter tank structure (although steel or other tank materials may be used) is begun, but not before it is finished. This involves considerable expense in mobilizing equipment on the site, demobilizing, and then remobilizing. The normal construction sequence typically occurs over a period of several months. Also, due to complexity of installation, the manufacturers of the parts of such filter systems are typically required to provide up to three weeks supervision during installation.
Another drawback is that the sealant requires considerable care in its application, as it is widely recognized that sealant problems are a leading cause of failure in waste water filter systems. Although sealing of the plates is critical to proper performance, it is frequently performed by unskilled workers unfamiliar with the equipment, and manufacturer supervision is seldom available for the entire duration of the installation.
The large amount of hardware required for cell assembly also contributes to improper construction of the underdrain. Additionally, grout between cells is problematic in that grout must be applied in narrow spaces, at a slope, and is difficult to clean up.
Should problems develop after start-up, disassembly and repair is extremely difficult. The use of sealant/adhesive during installation results in a large percent of breakage of the components when attempting to disassemble the filter.
This invention solves what has historically been perhaps the number one problem with such equipment: media leaks resulting from poor installation of the underdrain and porous plates.
This invention provides a integral plenum module that may be factory assembled and installed directly to a filter slab. This elimates the need for a technician to be on site during the construction of the plenum section of the filter.
This invention also elimates the need for installing leveling strips in order to provide a level base for the cell dividers.